The Northern Wars, 1558-1721 by Robert I. Frost; Longman, Harlow, England; 2000 ISBN 0-582-06429-5
Team Fortress 2 | Boeing B-17 Flying Fortress | Fortress of Louisbourg | Brest Fortress | Akershus Fortress | The Super Dimension Fortress Macross | Peter and Paul Fortress | Niš Fortress | Modlin Fortress | Defense of Brest Fortress | Nehaj Fortress | Miracle Fortress | Fortress Saint-Maurice | Fortress of Kaysun | Augsburg Fortress | Antonia Fortress | Warsaw Fortress | Varberg Fortress | ''The Memphis Belle: A Story of a Flying Fortress'' | The Hidden Fortress | Skopje Fortress | Sharpe's Fortress | Salacgrīva fortress | Real Felipe Fortress | Peter and Paul fortress | Osowiec Fortress | Norske Løve Fortress | Morro Castle (fortress) | Memphis Belle: A Story of a Flying Fortress | Kufstein Fortress |